Electrodepositing copper upon steel wire



y 1 47- o. E. ADLER 2,420,291

ELBG'I'RODBPOSITING COPPER UPON STBBL IIRE Filed July 22. 1940 & i 6%W48,

Patented May 13, 1947 ELECTRODEPOSITING COPPER UPON STEEL WIRE OrvilleE. Adler, Niles, Mich., assignor to National-Standard Company, acorporation of Michigan Application July 22, 1940, Serial No. 346,867

6 Claims. (01. 204-34) This invention relates to a method of producing acopper clad wire, and particularly a copper clad steel wire of very hightensile strength, which has been drawn after the application of thecopper to it.

Copper clad steel wires heretofore have been prepared in two differentways. In the earlier method a casting was prepared in which a large bodyof copper surrounded a billet or rod of steel. The whole material wasreduced to the proper size. It has also been suggested to electroplatecopper directly upon a finished wire.

Both of these methods were unsatisfactory for various reasons. Thedirect electroplating of copper upon a wire has lately come into favor,but this method is expensive. It does not result in uniform coppercoatings, and the wires necessarily employed for direct plating have avery low tensile strength.

In accordance with the present invention, a copper clad wire of highertensile strength than those previously produced and at the same timehaving a copper coating of great uniformity is produced.

The invention is illustrated diagrammatically in the drawings, in which:Figure 1 represents a cross section of wire before drawing; and Figure 2is a cross section of the wire after drawing.

The wire employed is preferably a high tensile strength, high carbonwire, for example, one

having a typical composition as follows:

Balance is iron, with cases of impurities.

The wire must be carefully cleaned before treatment. The followingexample illustrates a typical treatment for a 0.119 inch diameter wireof the above composition which has been patented and limed.

Wire having a diameter of 0.185 inch and of the same composition as thewire heretofore described, and double lead patented, was cleaned in 32%hydrochloric acid at a temperature of 150 F. for 8 minutes. Thetemperature should not be allowed to fall below 130 F., nor theconcentration of the acid below 20% if the desired dull white appearanceis to be obtained. The wire was then washed with cold running Water,after leaving the acid, and was then passed into a sodium cyanidesolution, in which it was immersed for 10 minutes. The solution was keptwithin the limits of 1 to 3 ounces of sodium cyanide per gallon,although these limits are not critical. The cyanide is preferably keptat room temperature but may be warm and may be used in conjunction withcurrent. This cyanide bath was used as a wash to neutralize any acidremaining on the wire and also to leave a protective film on the wirewhich does not have to be Washed off before the wire enters the cyanideplating bath.

The wire was passed from the cyanid wash into the cyanide copper platerand was plated at 30 amperes/sq. ft. The current density may beconsiderably higher but a higher amperage is not necessary. Preferablythe solution is operated at about 150 F. and kept at an analysis of 30to 40 grams per liter of copper, 15 to 25 grams per liter of freecyanide, 20 to grams per liter of sodium potassium tartrate, togetherwith carbonate as desired. The pH of the solution should be kept above11 and it should be free from hypo.

The described process gives a copper coating of 20 to 24 grams perkilogram of wire (0.00075 inch in thickness), but a minimum of about 3grams or approximately 0.0001 inch is sufiicient to provide an adherentcoating. The primary importance of this step is to coat all of the steelwith the cyanide deposited copper and if the wire has been properlycleaned it will assume a uniform coat immediately upon entering theplating solution.

The wire is then thoroughly washed and enters the acid copper platingsolution. It was plated at about 165 amperes/sq. ft. for 2 hours and 30minutes in this bath. While the analysis of the solution can varygreatly in the example, it consisted of grams per liter of copper and 75grams per liter of sulfuric acid. This particular bath combines maximumconductivity and cathode efficiency. The solution must be vigorouslyagitated with air during the plating. It is preferably maintained at F.Temperatures above F. develop a poor bond between the copper coatings.The presence of nickel, even in amounts as low as 0.2 gram per liter,produces a poor bond. In this bath a coating of 350 grams per liter wasapplied in the time specified, making a total thickness of 370 grams or0.0225 inch; The wire Was, therefore, increased to 0.230 inch indiameter and 33.6% of the cross section of the coated wire Was copper.

While current densities as high as 300 amperes/sq. ft. have been used inthe acid plating solutionwitheorrespondingdecreaseintimefor a thicknessof equal coating, the copper-deposit tends to become more brittle as thecurrent density appproachcs the higher ranges.

After the second plating operation the wirewaswashedandwasreadyi'ordrawing. 'Itwas then drawn, using soap as alubricant with a reduction of approximately per pass. Thewireinthlsexamplesuccessivelyreducedtothe following diameters: 0.208,0.195, 0.175, 0.156, 0.140, 0.125, 0.112, 0.100, 0.090 and 0.081.

The finished wire had a conductivity of 40%, a resistance of 3.97ohms/1000', and a tensile strength of 1170 lbs (227,000 lbs/sq. in.).

In mother case, wire having a diameter of 0.255 was coated as describedto increase its dimeter to 0.293 and was then drawn in successive stagesto 0.107. The resulting wire had a 30% conductivity and a tensilestrength of 253,- 000 lbs/sq. in.

As another example of the process, which is suitable primarily forsmaller wires, the wire is first run through a hot 32% hydrochloric acidbath for 1.25 minutes. The wire, upon leaving the acid bath, must beclean, crystalline in appearance, and silvery white. The acid should behot and at least 20% hydrochloric acid. If allowed to become dirty, orit used on too much wire, it becomes ineffective and leaves a carbonsmudge on the wire. Sulfuric and nitric acids leave such a smudge.Before entering the bath the wire is scraped, for instance with steelwool, and after leaving the solution is wiped with rags, and then washedwith water, and again wiped. The wire is then treated with an alkalinesolution, for example, an Oakite 42B solution, at the rate of two ouncesto a gallon at an advanced temperature, say 180' F. for about a minute.An Oakite solution is essentially an alkaline phosphate. It is thenwashed and wiped and run into a copper cyanide plating bath. This bathis suitably one containing 48 grams per liter of copper cyanide, gramsper liter of free cyanide, containing sodium carbonate as desired.

The solution should be free from ypo. in order to produce as largecrystals as possible. A suitable plating density is one of amperes/sq.ft.

Preferably the solution is operated at 150' F. or

thereabouts, and is kept circulating. The amount of copper plated inthis bath may be varied, but suitably is from 0.0002 inch upwards inthickness, for example approximately 0.0008 inch, .which may be procuredin about 5 minutes under the conditions specified. Even with a hypo-freesolution the crystals are very small compared to copper deposited froman acid bath. The plating in cyanide is quite slow so that, owing toreasons of economy, the amount of plating therein i preferably keptsmall. .Moreover, a layer which is too thick is too brittle todrawproperly.

The wire is then washed in cold water and rinsed in hot water.

The wire may then be washed in a sodium cyanide bath containing about 3ounces per gallon of NaCN at 150 F. for a short time. washed with water,treated with 5% hydrochloric acid, washed with water and wiped, and isthen passed into an acid copper plating bath.

Such a bath is suitably a blue vitriol so ution containing to grams perliter of copper and about grams per liter of sulfuric acid. A suitableplating density is 225 amperesper square foot at a temperature of F. Thebath is preferably agitated violently with air during the plating.

with the bath described the amount of copper deposited may be variedsubstantially at will. Ifasuccessimofcyclesis employedaplating time ofto 1% minutes is preferred. In this time approximately 0.0005 inch ofcopper is deposited. When only a pair of cyclesis employed the thicknessof this coating should be within approximately 0.000375 and 0.00075 inchof thickness. But if only two plating baths are used, then the coatingmay be much thicker.

In carrying out multiple cycles, after removalfromthebaththewireispassedthrougha water wash, then treated with 32%hydrochloric acid, after which it is again washed by running throughrags, again passed through an alkaline bath at a concentration ofapproximately 2 ounces per gallon at a temperature of 180" R,

again washed with water by running through rags, and then again placedin a copper cyanide plating bath.

Thisbathisthesameasthecyanidebath heretofore described, but the productis maintained in it only aboutone minute instead of live, during whichtime about 0.0001 inch of copper is deposited. The product is thenwashed with cold water, and then with hot water. The product may then bepassed through sodium cyanide solution. containing about 3 ounces pergallon at F. It is then washed with water, in 5% hydrochloric acid forseveral minutes, and i then washed with water by running through wateredrags for several minutes.

The product is then passed into the acid bath, as heretofore described,where it is copper plated for 38 minutes, during which timeapproximately 0.016 inch of copper is deposited. The product is thenwashed with water.

The thicknesses of copper given heretofore are upon the entire diameterof the wire and the thickness in each side is, therefore, one-half asmuch.

During the entire multiple plating operation described, the diameter ofthe wire increases by about 0.0165 or about 260 to 265 grams copper perkilogram of wire. The coating which is produced in the above describedmanner is very adherent, and will withstand a bend without breaking orcracking. It will also stand drawing without breaking or cracking.

When only one cycle is employed the cyanide coating may be any thicknessfrom about 0.0002 inch upwards. The acid coating will not adhere to thebase metal and therefore the cyanide coat should be enough to provide asuitable base. Ordinarily from 0.0008 inch to about 0.0020 inch ispreferred for the coating. The acid coating is then of sumcientthickness to give the desired conductive coating.

The wire is drawn down to final size in several steps. This may be doneon three or four pass continuous wire drawing machines employingCarboloy dies. Either steel drawing dies or copper drawing dies may beemployed. A preferred drafting procedure is as follows:

The 0.119 wire is first reduced to 0.104, then to 0.085, then to 0.072,then to 0.061, then to 0.051, then to 0.042. These fi ures are the sizeof the core only. At the end of the finishing speed of the wire ispreferably around 375 feet per minute. No unusual precautions arerequired.

After drawing, the tensile strength of the core will be found to be atleast 245,000 lbs/sq. in., as compared to a maximum of about 142,000lbs/sq. in. heretofore obtainable. The product also has a torsionbetween 60 and 80 for an 8 inch piece.

. The overall tensile strength of the copper coated wire will be atleast 210,000 lbs/sq. inch.

After drawing to final size, the wire may be hot-tinned in accordancewith the usual practice, being run through molten tin preferably at atemperature of about 500 F.

The finished wire has a resistance of 16.5 to 17.5 ohms/1000, and aconductance of 30%. It can be bent round its own diameter withoutbreaking or cracking. The thickness of the copper on each side of the0.045 inch wire was about 0.003 inch in the example given, and isuniform within 0.0004 inch from the average in any single cross section.Much greater thicknesses may be produced if desired.

The copper, when first applied, has a matte finish and is porous. Whendrawn, however, it is bright, hard, and continuous and maybe bent uponits own diameter.

In all cases the conductivity is at least Instead of the cycles hereshown, additional alternatives may be employed, but are unneces- Sary.

. This application is a continuation-in-part of application, Serial No.238,278, filed November 1, 1938, now Patent No. 2,317,350, Apr. 27,1943.

The foregoing detailed description is given for clearness ofunderstanding only, and no unnecessary limitations should be understoodtherefrom.

What I claim as new, and desire to secure by Letters Patent, is:

1. The method of forming a copper clad wire which comprises cleaning aferrous wire in a hot clean bath of hydrochloric acid having aconcentration not substantially less than to produce a silvery whitecrystalline appearing surface, electro-depositing upon such surface fromthe cyanide bath a firmly adherent layer of copper, andelectro-depositing upon the cyanide copper a firmly adherent layer ofcopper from an acid bath.

2. The method of producing a drawn copper clad steel wire having hightensile strength and a conductive copper outer coating which comprisescleaning the steel wire in an acid to produce a silvery whitecrystalline appearing clean surface thereon, progressively passing theclean wire into an alkaline cyanide copper-plating bath andelectroplating thereon an adherent thin coating of copper, removing thewire progressively from the bath. removing residual cyanide solutiontherefrom, then progressively introducing the wire into an acidcopper-plating bath and forming a relatively thick layer of porous mattecopper thereon and then drawing the composite copper articlesubstantially to reduce its diameter, thereby altering the porous mattecopper to a bright hard continuous electro=conductive coating, thecopper being thick enough to produce a conductivity of at least 15% in.the drawn wire.

245,000 lbs. per square inch and having thereon a hard continuous coppercoating at least about 0.003 inch in thickness and produced by themethod of claim 2.

5. A copper clad steel wire having a conductivity of at least 15% andhaving a central steel core having a tensile strength of at least245,000 lbs. per square inch and having thereon a hard continuous coppercoating at least about 0.003 inch in thickness and produced by themethod of claim 2.

6. The method which comprises cleaning a ferrous wire in a hot cleanbath of hydrochloric acid having a concentration of not substantiallyless than 20 per cent, then progressively passing the clean wire throughan alkaline cyanide bath and electrodepositing thereon a firmly adherentlayer of copper having a thickness of at least .0001 inch and not morethan .0004 inch, cleaning the copper plated wire to remove the cyanideand progressively passing the wire through an acid copper plating bathand depositing thereon -a heavy layer of copper having a thickness of atleast .002 inch, the total amount of copper on the wire being sumcientto give a conductivity of over 15 per cent.

ORVILLE E. ADLER.

REFERENCES EDITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,322,494 Merritt Nov. 18, 19191,601,982 Romanelli Oct. 5, 1926 61,143 Bernohe Jan. 15, 1867 64,135Parar Apr. 23, 1867 1,992,244 Schuricht Feb. 26, 1935 2,268,617 PierceJan. 6, 1942 2,196,002 Whitney Apr. 2, 1940 2,317,350 Adler et a1. Apr.27, 1943 FOREIGN PATENTS Number Country Date 12,720 Great Britain of1849 18 Great Britain of 1855 25,393 Great Britain -1 of 1913 OTHERREFERENCES Blum & Hogaboom, Principles of Electroplating, etc. (1930),2nd ed., pub. by McGraw-Hill Book (20., N. 2., pp. 149, 150. (Copy inDiv. 56.)

